1. Field of the Invention
The present invention relates to a novel, advantageous and economic process of upgrading waste paper and especially printed waste paper by means of a flotation de-inking process so as to remove therefrom the printing ink or other printing matter, to de-inking compositions and baths used in said process, and to reclaimed waste paper upgraded by said process.
2. Description of the Prior Art
In view of the ever increasing world-wide scarcity in wood supply and the continuously increasing energy costs, upgrading and re-using of waste paper has attained greater and greater importance. Yet an increase in the use of reclaimed waste paper is highly dependent on an improvement in the quality of the reclaimed waste paper, more particularly an improvement of its optical properties, i.e. of its degree of whiteness. To regenerate said valuable raw material, there have been developed de-inking processes which have been used extensively in industry during the last decades. The washing and flotation process for the separation of the printing ink particles from the suspension of fibers and filler materials in the waste paper pulp has proved to be of special value. Said flotation de-inking process is described, for instance, in "DAS PAPIER", vol. 10 A, (1961), pages 546 to 554. This process is based on the differences in wettability of the printing ink particles to be removed from the fiber suspension, and the fiber particles. When carrying out this process, one must attempt to separate and remove the printer's ink as thoroughly as possible. This effect and result are achieved by loosening and separating the printing ink particles from the fiber material by means of suitable chemical agents and causing them to float by introducing air into the suspension. Alkali metal salts of fatty acids, surfactants, such as, for instance, ethoxylated fatty acids or alkyl phenyl sulfonates, which, conventionally act as dispersing agents, as well as complex compound-forming agents, such as ethylene diamine tetraacetic acid are used as flotation aids. Alkali metal peroxides, such as sodium peroxide, or, respectively, hydrogen peroxide and alkali metal hydroxide solutions, such as sodium hydroxide solution, and waterglass as stabilizer for the peroxide are also added as chemical de-inking agents. A suitable de-inking composition thus may be composed as follows:
______________________________________ Sodium peroxide or hydrogen peroxide 1.0%-2.0%, waterglass 1.0%-5.0%, fatty acid 0.6%-1.2%, complex compound-forming agents such as ethylene diamine tetra-acetic acid 0.2%-0.4%, sodium hydroxide 0.0%-2.0%, dispersing agent 0.1%-0.2%. ______________________________________
The manner in which the known de-inking process is carried out is described in numerous literature references. The following articles may be mentioned as examples:
Bechstein, G. "Der Deinking-Flotationsprozess, ein modernes Verfahren der Altpapier-Aufbereitung" (The de-inking process, a modern procedure for reclaiming waste pater), published in "Zellstoff und Papier" vol. 22 (1973), No. 11, pages 337-339;
Ortner, H., Wood, R. F., Gartemann, H. "Deinking--Stand Entwicklung" (De-inking--status and development) published "Wochenblatt fuer Papierfabrikation", No. 16, pages 597-601;
Weidhaas, A. G. "Erfahrungen mit einer De-inking-Anlage zur Erzeugung von Zeitungsdruckpapier" (Experiences with a de-inking plant for producing newsprint paper) published in "Wochenblatt fuer Papierfabrikation" vol. 104 (1976), No. 22, pages 857-865; and
Schlaepfer, K., Faessler, U., Kueng, P. "Der Einfluss der Druckfarbe beim Deinking von Zeitungspapier" (The influence of the printing ink on the de-inking of paper used for newsprint paper), "UGRA-Auftrag 68" (UGRA Order 68), UGRA: Verein zur Foerderung wissenschaftlicher Untersuchungen im graphischen Gewerbe, 1974, St. Gallen.
When carrying out the known processes, there are encountered considerable difficulties which are caused by the addition of waterglass added as stabilizing agent for the peroxide. Silicate deposits precipitate in the pipelines of the de-inking system and also in the sieves, felts, and calenders of the paper machine. The de-inked paper pulp or slurry to which waterglass has been added, also causes trouble on the paper machine during dewatering or drying, because waterglass reduces very considerably the action of retention affecting agents and of dewatering accelerators. The waste water from the de-inking plant can be clarified and purified only with difficulty by the addition of flocculating agents due to its high content of waterglass. Another disadvantage of the heretofore used de-inking processes resides in the fact that the paper pulp to which waterglass has been added, yields reclaimed paper which shows losses in strength and tends to turn yellowish.